Google and Twitter have also investigated Russian-backed content appearing on their sites.

Most of the posts focused on sowing political and social divisions, the firms have said.

Google said it is developing tools to make more information about the buyers of political ads available to the public.

What is Facebook saying?

Facebook says some 80,000 posts were published between June 2015 and August 2017 and were seen by about 29 million Americans directly, according to a draft of prepared remarks seen by US media ahead of Tuesday’s Senate judiciary committee hearing.

These posts, which Facebook says were created by a Kremlin-linked company, were amplified through likes, shares and comments, and spread to tens of millions of people.

Facebook also said it had deleted 170 Instagram accounts, which posted about 120,000 pieces of content.

“These actions run counter to Facebook’s mission of building community and everything we stand for,” Facebook’s general counsel Colin Stretch said on Tuesday.

“And we are determined to do everything we can to address this new threat.”

In a blog post from earlier this month, Facebook’s Elliot Schrage said that many of the posts did not violate the company’s content policies. They were removed, he said, because they were inauthentic – the Russians behind the posts did not identify themselves as such.